2-Hy­dr­oxy-7-nitro­cyclo­hepta-2,4,6-trien-1-one

The title compound, also known as 7-nitro­tropolone, C₇H₅NO₄, exists in the crystalline state as the 2-hy­droxy-7-nitro­cyclo­hepta-2,4,6-trien-1-one tautomer and not as 2-hy­droxy-3-nitro­cyclo­hepta-2,4,6-trien-1-one. The dihedral angle between the ring and the nitro group is 70.3 (2)°. In the crystal, neighbouring mol­ecules are linked into dimers by a pair of O—H⋯O hydrogen bonds. In addition, the crystal is stabilized by O⋯π [3.4039 (14) Å] and O⋯O [3.073 (2) Å] inter­actions.

Related literature

For the structure of tropolone and 5-nitro­tropolone, see: Shimanouchi & Sasada (1973); Kubo et al. (2001), respectively. Structural data on other mono-substituted tropolones were reported by Derry & Hamor (1972); Berg et al. (1976); Tsuji et al. (1991); Kubo et al. (2001, 2006a,b, 2007a,b,c,d). For the synthesis of nitro­tropolone, see Cook et al. (1954).

Experimental

Crystal data

• C₇H₅NO₄

• M_r = 167.12

• Monoclinic, P 2₁ /c

• a = 9.6167 (2) Å

• b = 6.4772 (1) Å

• c = 11.7326 (4) Å

• β = 96.162 (2)°

• V = 726.59 (3) ų

• Z = 4

• Cu Kα radiation

• μ = 1.11 mm⁻¹

• T = 295 K

• 0.45 × 0.35 × 0.15 mm

Data collection

• Agilent SuperNova (Dual, Eos) diffractometer

• Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2010) T_min = 0.541, T_max = 1.000

• 8694 measured reflections

• 1364 independent reflections

• 1314 reflections with I > 2σ(I)

• R_int = 0.022

Refinement

• R[F² > 2σ(F²)] = 0.038

• wR(F²) = 0.106

• S = 1.07

• 1364 reflections

• 113 parameters

• H atoms treated by a mixture of independent and constrained refinement

• Δρ_max = 0.19 e Å⁻³

• Δρ_min = −0.16 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H2⋯O1	0.84 (3)	2.05 (3)	2.5796 (14)	120 (2)
O2—H2⋯O1^i	0.84 (3)	2.04 (3)	2.7349 (15)	139 (3)
Symmetry code: (i) -x, -y, -z.

Data collection: CrysAlis PRO (Agilent, 2010); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97.

Supporting information

S1. Comment

The aim of the present work was to determine the structure of the second isomer of nitrotropolone which is formed besides 5-nitrotropolone in the nitration reaction described by Cook et al. (1954). The second purpose was to find out which of the possible tautomers, 2-hydroxy-7-nitrocyclohepta- 2,4,6-trien-1-one or 2-hydroxy-3-nitrocyclohepta-2,4,6-trien-1-one is present in the solid state. It appeared that three different compounds were obtained during the nitration process with 7-nitrotropolone (Fig. 1) and 5-nitrotropolone as the main products and 7-hydroxytropolone as the side product.

In the title compound the C2—O2 bond (1.3324 (17) Å) is longer than the C1—O1 bond (1.2403 (16) Å). In combination with the features of the difference Fourier map this allows the unambiguous location of the hydroxyl H atom as bonded to the O2 atom. According to the rule which assigns position 1 in the tropolone ring to the carbon atom of the carbonyl group and position 2 to the carbon atom bonded to the hydroxyl group, the crystallized compound is 7-nitrotropolone and not 3-nitrotropolone.

The crystal structures of tropolone (Shimanouchi & Sasada, 1973) and other mono-substituted tropolones, such as 5-nitro-, 5-cyano- (Kubo et al., 2001), 5-methyl- (Kubo et al., 2007b), 5-methoxy- (Kubo et al., 2006b), 5-acetoxy- (Kubo et al., 2006a), 5-iodo- (Kubo et al., 2007d), 7-iodo- (Kubo et al., 2007c), 4-isopropyl- (Derry & Hamor, 1972), 5-isopropyl- (Berg et al., 1976), 7-hydroxy- (Kubo et al., 2007a), 7-chlorotropolone (Tsuji et al., 1991), have been reported previously.

The studied compound forms centrosymmetric O—H···O hydrogen-bonded dimers, similar to those found for 5-nitrotropolone (Kubo et al., 2001), tropolone (Shimanouchi & Sasada, 1973) and the most of its mono-substituted derivatives. Some of the other derivatives of tropolone, e.g. 4-isopropyltropolone (Derry & Hamor, 1972), 5-iodotropolone (Kubo et al., 2007d) and 7-iodotropolone (Kubo et al., 2007c), form hydrogen-bonded zigzag chains. The crystal structure of the title compound contains molecules linked into dimers through intermolecular O—H···O hydrogen-bonds involving the OH groups and the carbonyl O atoms (Table 1, Fig. 2). The hydroxyl group is in fact involved in a bifurcated hydrogen bond that also forms an intramolecular link to the carbonyl acceptor in the same molecule. The intermolecular distance O1···O2 of 2.7349 (15) Å is similar to that found for 5-nitrotropolone (2.743 Å, Kubo et al., 2001) and tropolone (2.746 Å, Shimanouchi & Sasada, 1973). Intermolecular interactions between the hydroxyl group and a seven-membered ring (O—H···π interactions) are also observed; the O2···C(1–7)ⁱⁱ [symmetry code: (ii) -x, 1 - y, -z] distances are in the range 3.585–3.637 Å. Furthermore, interactions between the nitro group and neighbouring rings of tropolone molecules (O···π interactions) are observed in the crystal structure: 3.149 Å for O4···C2ⁱⁱⁱ, 3.321 Å for O4···C3ⁱⁱⁱ, 3.472 Å for O4···C1ⁱⁱⁱ [symmetry code: (iii) x, 1/2 - y, 1/2 + z], 3.430 Å for O4···C4^iv [symmetry code: (iv) x, 3/2 - y, 3/2 + z] and 3.499 Å for O3···C6^v [symmetry code: (v) 1 - x, -1/2 + y, 1/2 - z]. The closest distance between symmetry related tropolone planes is 3.272 Å for C2···C2ⁱⁱ. However, the intermolecular π···π interactions between neighbouring rings are much less distinct in the crystal structure of 7-nitrotropolone than for 5-nitrotropolone (Kubo et al., 2001). The shortest contact between oxygen atoms from neighbouring NO₂ groups is 3.073 Å for O3···O4^v. All of the interactions mentioned above have an influence on the formation of crystal structure network (Fig. 2). In 5-nitrotropolone (Kubo et al., 2001) all atoms of the NO₂ group lie exactly in (torsion angle C6—C5—N1—O4 0.2 (2)°) or very closely to (torsion angle C13—C12—N1—O7 13.7 (2)°) the plane of the tropolone ring while for the 7-nitrotropolone this group is rotated out of the tropolone plane (torsion angle C1—C7—N1—O3 71.5 (2)°).

Related literature

For the structure of tropolone and 5-nitrotropolone, see Shimanouchi & Sasada (1973) and Kubo et al. (2001), respectively. Structural data on other mono-substituted tropolones were reported by Derry & Hamor (1972); Berg et al. (1976); Tsuji et al. (1991); Kubo et al. (2001, 2006a,b; 2007a,b,c,d). For the synthesis of nitrotropolone, see Cook et al. (1954).

S2. Experimental

The title compound and 5-nitrotropolone were synthesized together as the main products in the nitration reaction of tropolone described by Cook et al. (1954). 7-hydroxytropolone was also obtained in this reaction but in a much smaller amount. Single crystals of these compounds were found after recrystallization from benzene. The formation of these products were confirmed by single-crystal X-ray diffraction measurements.

S3. Refinement

The H atom of the OH group was located in a difference map and its position and U_iso value were freely refined. All H atoms bonded to C atoms were placed in calculated positions with C—H = 0.93 Å and refined isotropically using riding model with U_iso(H) = 1.2 U_eq(C).

Computing details

Data collection: CrysAlis PRO (Agilent, 2010); cell refinement: CrysAlis PRO (Agilent, 2010); data reduction: CrysAlis PRO (Agilent, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al. 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. Molecular structure of the title compound. Displacement ellipsoids of the non-hydrogen atoms are drawn at the 50% probability level.
	Fig. 2. A fragment of the crystal structure showing the hydrogen bonds and intermolecular interactions in the 7-nitrotropolone. Dashed lines indicate hydrogen bonds and other intermolecular interactions.

2-Hydroxy-7-nitrocyclohepta-2,4,6-trien-1-one

Crystal data

C7H5NO4	F(000) = 344
Mr = 167.12	Dx = 1.528 Mg m^−3
Monoclinic, P21/c	Cu Kα radiation, λ = 1.54178 Å
Hall symbol: -P 2ybc	Cell parameters from 6294 reflections
a = 9.6167 (2) Å	θ = 3.8–72.1°
b = 6.4772 (1) Å	µ = 1.11 mm^−1
c = 11.7326 (4) Å	T = 295 K
β = 96.162 (2)°	Plate, yellow
V = 726.59 (3) Å^3	0.45 × 0.35 × 0.15 mm
Z = 4

Data collection

Agilent SuperNova (Dual, Eos) diffractometer	1364 independent reflections
Radiation source: SuperNova (Cu) X-ray Source	1314 reflections with I > 2σ(I)
Mirror monochromator	Rint = 0.022
Detector resolution: 16.0131 pixels mm^-1	θmax = 70.0°, θmin = 7.6°
ω scans	h = −11→11
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2010)	k = −7→7
Tmin = 0.541, Tmax = 1.000	l = −14→13
8694 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.106	H atoms treated by a mixture of independent and constrained refinement
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0534P)^2 + 0.1985P] where P = (Fo^2 + 2Fc^2)/3
1364 reflections	(Δ/σ)max < 0.001
113 parameters	Δρmax = 0.19 e Å^−3
0 restraints	Δρmin = −0.16 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.16992 (13)	0.2812 (2)	0.03140 (11)	0.0391 (3)
C2	0.10047 (15)	0.3639 (2)	−0.07541 (11)	0.0427 (3)
C3	0.12800 (17)	0.5388 (2)	−0.13382 (13)	0.0530 (4)
C4	0.22824 (19)	0.6924 (3)	−0.10795 (15)	0.0600 (4)
C5	0.32680 (19)	0.7082 (3)	−0.01626 (16)	0.0613 (5)
C6	0.35254 (16)	0.5684 (2)	0.07413 (14)	0.0535 (4)
C7	0.28716 (13)	0.3865 (2)	0.09138 (11)	0.0416 (3)
H2	−0.011 (3)	0.146 (4)	−0.077 (2)	0.101 (9)*
H3	0.0707	0.5589	−0.2019	0.064*
H4	0.2275	0.7992	−0.1610	0.072*
H5	0.3833	0.8250	−0.0134	0.074*
H6	0.4241	0.6046	0.1302	0.064*
N1	0.34481 (12)	0.2721 (2)	0.19480 (11)	0.0500 (3)
O1	0.12366 (11)	0.11924 (15)	0.06932 (9)	0.0534 (3)
O2	−0.00635 (12)	0.24914 (19)	−0.12093 (9)	0.0568 (3)
O3	0.40798 (16)	0.1136 (2)	0.18063 (12)	0.0853 (5)
O4	0.32868 (16)	0.3421 (2)	0.28807 (10)	0.0751 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0399 (7)	0.0356 (7)	0.0401 (7)	−0.0002 (5)	−0.0038 (5)	−0.0029 (5)
C2	0.0472 (7)	0.0425 (7)	0.0367 (7)	0.0006 (6)	−0.0031 (5)	−0.0048 (5)
C3	0.0655 (9)	0.0517 (9)	0.0404 (7)	0.0028 (7)	−0.0011 (6)	0.0057 (6)
C4	0.0757 (11)	0.0452 (9)	0.0603 (10)	−0.0017 (8)	0.0125 (8)	0.0114 (7)
C5	0.0628 (10)	0.0438 (8)	0.0777 (12)	−0.0129 (7)	0.0091 (8)	0.0015 (8)
C6	0.0463 (8)	0.0496 (8)	0.0626 (9)	−0.0102 (6)	−0.0036 (6)	−0.0074 (7)
C7	0.0379 (7)	0.0418 (7)	0.0433 (7)	0.0003 (5)	−0.0041 (5)	−0.0036 (5)
N1	0.0433 (7)	0.0532 (7)	0.0500 (7)	−0.0057 (5)	−0.0109 (5)	−0.0016 (5)
O1	0.0569 (6)	0.0433 (6)	0.0551 (6)	−0.0128 (5)	−0.0164 (5)	0.0074 (4)
O2	0.0653 (7)	0.0564 (7)	0.0433 (6)	−0.0133 (5)	−0.0188 (5)	0.0017 (5)
O3	0.0887 (10)	0.0850 (10)	0.0759 (9)	0.0384 (8)	−0.0202 (7)	0.0027 (7)
O4	0.1024 (10)	0.0742 (9)	0.0475 (7)	−0.0110 (7)	0.0025 (6)	−0.0021 (6)

Geometric parameters (Å, º)

C1—C7	1.4358 (18)	C6—H6	0.9300
C2—C1	1.4575 (18)	C7—C6	1.361 (2)
C2—C3	1.364 (2)	N1—O3	1.2135 (19)
C3—H3	0.9300	N1—O4	1.2098 (17)
C4—C3	1.396 (2)	N1—C7	1.4779 (18)
C4—C5	1.359 (3)	O1—C1	1.2403 (16)
C4—H4	0.9300	O2—C2	1.3324 (17)
C5—H5	0.9300	O2—H2	0.84 (3)
C6—C5	1.396 (2)
C1—C7—N1	111.71 (12)	C6—C7—C1	133.59 (14)
C2—O2—H2	106.8 (19)	C6—C7—N1	114.68 (12)
C2—C3—C4	130.48 (14)	C7—C1—C2	120.66 (12)
C2—C3—H3	114.8	C7—C6—C5	128.85 (15)
C3—C2—C1	129.91 (13)	C7—C6—H6	115.6
C3—C4—H4	115.4	O1—C1—C2	118.07 (12)
C4—C3—H3	114.8	O1—C1—C7	121.26 (12)
C4—C5—C6	127.17 (15)	O2—C2—C1	113.69 (12)
C4—C5—H5	116.4	O2—C2—C3	116.41 (13)
C5—C4—C3	129.22 (15)	O3—N1—C7	117.45 (13)
C5—C4—H4	115.4	O4—N1—C7	118.79 (13)
C5—C6—H6	115.6	O4—N1—O3	123.76 (15)
C6—C5—H5	116.4
C1—C2—C3—C4	−1.6 (3)	O1—C1—C7—C6	−175.17 (15)
C1—C7—C6—C5	−4.0 (3)	O1—C1—C7—N1	3.12 (19)
C2—C1—C7—C6	3.9 (2)	O2—C2—C1—C7	179.96 (12)
C2—C1—C7—N1	−177.80 (11)	O2—C2—C1—O1	−0.93 (19)
C3—C2—C1—C7	−0.5 (2)	O2—C2—C3—C4	178.01 (16)
C3—C2—C1—O1	178.65 (15)	O3—N1—C7—C1	71.52 (17)
C3—C4—C5—C6	1.4 (3)	O3—N1—C7—C6	−109.84 (17)
C5—C4—C3—C2	0.2 (3)	O4—N1—C7—C1	−109.60 (15)
C7—C6—C5—C4	0.4 (3)	O4—N1—C7—C6	69.04 (18)
N1—C7—C6—C5	177.76 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1	0.84 (3)	2.05 (3)	2.5796 (14)	120 (2)
O2—H2···O1^i	0.84 (3)	2.04 (3)	2.7349 (15)	139 (3)

Symmetry code: (i) −x, −y, −z.